Introduction

Here we record our work on the development, improvement, and quality assurance of our Subcutaneous Transmitters. We begin with a summary table showing the results of our accelerated aging reliability testes. We present the various circuit board versions we have made in our pursuit of ease and reliability of encapsulation. Our day-to-day record of work starts with the introduction of the A3028 transmitter in September 2013. For earlier records of development, see A3019 (2010-2014), and A3013 (2007-2011) manual pages. For early work on encapsulation see SCT Encapsulation. For radio frequency isolation see Faraday Enclosures. For flexible leads see Flexible Wires. For comparison of electrodes see Electrodes. For work on radio frequency reception see Data Transmission and Reception.

Accelerated Aging

[29-MAR-17] We started accelerated aging tests after discovering that a lot of one hundred A3028AV2 circuits was plagued by cracked capacitors as a result of excessive placement force during automated assembly. In the warmth and humidity of an animal's body, these cracks corroded and caused the capacitors to fail within a few days of implantation. Such corrosion takes place more quickly at higher temperatures, as presented in Hallberg and Peck. We began accelerated aging test in March, 2015. Since then, we have poached roughly one hundred transmitters in hot water until they failed by one means or another.

According to statistical mechanics, the rate at which a chemical reaction proceeds is proportional to e−E/kT, where T is absolute temperature, E is the activation energy of the rate-determining step in the chemical reaction, and k = 8.6×10−5 eV is the Boltzmann constant. We expect the mean time to failure of our subcutaneous transmitters to be proportional to eE/kT.
In Hallberg and Peck, the authors show that this relationship applies well to measurements of the mean time to failure for temperatures 20-150 °C and relative humidity 20%-100% when they use an activation energy of 0.9 eV. Their measurements came from studies of circuits assembled with tin-lead solder. For modern circuits, which are usually made with silver-tin solder, a better value for the activation energy may be 1.1 eV. The higher the value of E, the greater the acceleration of aging at a higher temperature. We assume an activation energy of 0.9 eV for corrosion in our circuits, so as to give us a conservative estimate of the acceleration caused by poaching at higher temperatures. Our devices operate at the rodent body temperature of 37°C = 310 K. When we perform an accelerated aging test at 60°C = 333 K, we expect an acceleration of at least ×10. At 80°C = 353 K we expect acceleration of at least ×60.

The following table summarizes our recent accelerated aging tests. For older tests see our archives. All tests in water in a sealed jar. Failures recorded on the day they are first detected. An "artifact" is a severe corruption of the EEG signal that appears after the start of the test. Examples of severe corruption are: gain versus frequency for 100-kΩ source is wrong by more than 3 dB, steps changes of ≥100 μV once every ten seconds, dynamic range compressed to less than 10 mV. A "failure" is a failure to transmit an EEG signal, however corrupted that signal might be by artifacts. Search the notes below with the transmitter serial number to get the details of each transmitter we poached.

Table: Summary of Accelerated Failure Tests. The circuit problems are identified by two-letter codes. FL is "Full Life", RS is "Resistive Switch", CC is "Corroded Capacitor", CS is "Corrosion Short", CD is "Cavity Drain", UD is "Unidentified Drain", GE is "Gain Error", TM is "Transmit Malfunction", TS is "Temporary Shutdown", OG is "Out Gassing", FE is "Faulty Encapsulation". Time until we discovered the failure is after the failure code. If the poached transmitter had artifact problems at the beginning of the test, we enter "NA" for the first artifact time.

In the first tests, we did not take note of how we cooled the devices when we removed them from the oven to check them. In some tests we deliberately put them straight into cold tapwater to cool them rapidly. When three such transmitters failed within minutes of cooling, we suspected that thermal shock was a factor in the failures. For several months, we removed the devices from their poaching water and let them cool in air before testing. The resistive switch problem persisted, however, which suggests it is caused by condensation, not contraction. The resistive switch problem turned out to be due to dendrites growing between the pins of U1. We no longer take any particular precautions heating and cooling transmitters to and from 60°C, but we monitor their behavior during and after such changes, so as to catch failures that occur during expansion or condensation.

[15-NOV-16] Seven dual-channel A3028A mouse transmitters provided full performance in 80°C water for 11 days, during which corrosion equivalent to at least 660 days at 37°C took place. Four single-channel A3028E rat transmitters survived corrosion equivalent to at least 940 days at 37°C over the course of ten weeks at 60°C and 80°C. We conclude that that our transmitters will survive corrosion within an animal body for two years. This corrosion lifetime is separate from the operating life of the battery, which is set by the battery capacity and the transmitter's current consumption.

Circuit Versions

Aside from the assembly versions, we have versions of the circuit board that we use to build the A3028. The same circuit version can be used to make multiple assembly versions. The same assembly version can be constructed using multiple circuit versions. Here we list the more recent versions, the name of the printed circuit board they use, the type of capacitor, and what we know about the component assembly process.

Table: Summary of Circuit Board Versions. Links are to bills of materials.

The GV1 comes ready-made from the assembly house for single-channel 160-Hz and single-channel 80-Hz transmitters, both 1.4-ml and 2.8-ml sizes. The GV1 eliminates the mosfet power switch present on earlier versions, which turned out to be redundant, and which was the source of the "resistive switch" failure in accelerated aging. The GV1 provides a total of 40 μF of decoupling on the battery voltage, which reduces switching noise down to below 1 μV rms in encapsulated transmitters. The GV1 offers input protection, which has no significant effect upon the recording of EEG, but which guarantees that the circuit will not be endangered by stimulation voltages applied to the brain near the EEG electrodes.

2013

2014

2015

2016

2017

JAN-17

[03-JAN-17] Poaching transmitters: B146.8 and B146.9 have perfect frequency response. C111.3 gives good reception but generates a square wave. We turn them off and put them back in the oven.

We have B130.1, B130.4, B125.7, B130.8, B130.10, and B129.12 returned from IIT/Genova. We soak in water for an hour. According to IIT, these devices were implanted 5 weeks after they were shipped, worked upon implantation, were left turned off for ten days implanted, then failed to turn on. We attempt to turn on and off all six devices. Only B129.12 turns on. Reception is 100%, VA = 2.62 V, noise 8 μV. Frequency response is perfect. Silicone and epoxy like new. We place B129.12 in the oven to poach at 60°C turned off. In the remaining five devices, the epoxy coating was thin over corners of U9, U4, and U8. The silicone has pulled the epoxy coating off these corners, leaving an imperfection beneath the silicone. Some devices have wrinkles in the first of four coats of MED10-6607 silicone. By looking at the reflection of our overhead lights in the convex surface of the silicone coating, we confirm that the outer coat of silicone is everywhere intact and unbroken except around the base of the wire we used to hold the transmitters epoxy encapsulation in devices B130.10 and B130.4. On these two devices we see white oxide on the tip of this wire and also on the exposed solder joints of the antenna and leads. Dissect B130.10. Silicone well-adhered to epoxy. Green residue on positive battery tab. Battery voltage = VB = 0.1 V. Disconnect VB = 0.1 V. Connect external 2.6 V. Inactive current 2.0 μA, active 81 μA. Frequency response correct. Dissect B130.1. Silicone well-adhered. VB = 0.2 V. Disconnect, VB = 0.2 V. Apply external 2.6 V. Inactive 2.0 μA. Active 78.4 μA. Frequency response correct, see B130_5mV_2 for comparison of frequency response of these three transmitters just before shipping (1) and today when powered by an external battery (2). We place B130.4, B125.7, and B130.8 in water at 60°C and will dissect at a later date.

[06-JAN-17] Poaching transmitters: B129.12, B146.8 and B146.9 remove from water and turn on. All three have 100% reception. After cooling down, B146.9 shows steps changes of several millivolts. These become less common as minutes go by, allowing us to measure frequency response No9_3 in plot. The gain of B129.12 and B146.8 are correct (No12_3 and No8_3 in plot), but B146.9 is 6 dB too low at 100 Hz. When we switch to a 50-Ω 10-mV source, the gain is correct. C111.3 turn on and obtain 100% reception with 0.5-Hz square wave.

Dissect B130.4, no sign of corrosion, silicone in excellent condition. When we peel the silicone away we smell vinegar. VB = −0.2 V. Short the battery briefly, VB = 0.0 V. Disconnect, VB = −0.1 V. Connect external 2.6 V. Inactive 1.7 μA, active 78 μA. Reception 100%. Pick up mains hum. At first we see step artifacts, but after a few minutes these cease and we measure frequency response, which is perfect with 50-Ω source, but 10 dB too low at 100 Hz with 10-MΩ source (No4 in here). Dissect B125.7. No signs of corrosion, silicone is in excellent condition. We smell vinegar. VB = 0.1 V. Disconnect, VB = 0.1 V. Connect external 2.6 V, inactive 1.8 μA, active 78 μA, but fluctuating to 90 μA. Reception 100%. At first, we see a full-scale 0.5-Hz square wave. After a few minutes, this stops. Gain is 20 dB too low with both 50-Ω and 10-MΩ sources. Noise is 3 μV rms total. Dissect B130.8. No sign of corrosion. A few cavities beneath the silicone, but no breaches. No smell of vinegar. VB = −0.05 V. Disconnect, VB = −0.05 V. Connect external 2.6 V. Inactive 1.9 μV, active 78 μV then varying from 100 μA to 140 μA. Reception 100%, full-scale settling to 130 μA rising to 130 μA. We see full-scale oscillations at 110 Hz. We heat up C5 and current consumption stabilizes at 78 μA. Top of U5 is exposed, after cracking off of thin layer of epoxy. This the largest cavity that existed beneath the silicone.

[10-JAN-17] With a sanding wheel, we grind away the glue from the bottom side of B130.10 to check for penetration of epoxy around and beneath component terminals. So far as we can tell, epoxy penetrated everywhere, beneath and around the pins and bodies of all ICs, and beneath P0402 parts.

[17-JAN-17] Poaching transmitters: B129.12, B146.8, and B146.9 remove from water and turn on, all three have 100% reception and perfect response to 50-Ω sinusoidal sweep. With electrodes open circuit, all three detect mains hum, but B146.0 also produces occasional step and swings of order millivolts. C111.3 has gain 20 dB too low at 100 Hz with 50-Ω source and generates square wave with electrodes open circuit.

[20-JAN-17] We have batch L147 consisting of eight of A3028L-DDA. Frequency response L147_5mV agree to ±0.4 dB. Switching noise less than 2 μV, noise less than 14 μV.

[24-JAN-17] We have batch E145 consisting of 14 A3028E-AA. Some of these are particularly thick, with volume as high as 3.9 ml. Three that were so thick we sanded them down on the top side, are now 3.7 ml with a single coat of silicone. In May 2016 the A3028E volume was 3.0 ml. Frequency response E145_5mV within ±0.8 dB. Switching noise in water at 37°C is ≤4 μV, total noise ≤12 μV.

[27-JAN-17] We have batch A148 consisting of 7 A3028A-DDC. Gain versus frequency A148_5mV within 0.5 dB. Switching noise in 36°C water is &leg;4 μV. Noise ≤12 μV after ten minutes in water and after scrubbing some of the electrodes.

[30-JAN-17] We have batch A149 consisting of 4 A3028A-DDC. Gain versus frequency A149_5mV within 0.2 dB. Switching noise in 40°C water is &leg;4 μV. In A147.13 we have 4 μV in channel No14, but ≤ 1 μV in No13. We see rumble and some step artifacts when we first put the transmitters in water. Noise ≤12 μV in band 2-256 Hz after ten minutes.

FEB-17

[01-FEB-17] We have our first A3028M-AAA, a dual channel 0.3-640 Hz transmitter with 2048 SPS per channel. Current consumption is 442 μA. We have batch E150 consisting of fourteen A3028E-AA. Volume of four of them together is 12 ml. Another six together are 20 ml. In both cases, we are including the base of the antenna and leads. Our estimate of the volume of the body alone remains 3.0 ml. Frequency response is E150_5mV within ±0.4 dB. Switching noise in water at 36°C is E150_SWN.png all ≤5 μV. Total noise is less than 12 μV in 1-256 Hz. There is no rumble in the signal nor step artifacts from the moment we place the transmitters in water. These transmitters have bare-wire ends. Batch A148/9 had soldered electrodes and we observed large step artifact and rumble when we immersed them in water.

[07-FEB-17] We have batch N151 consisting of 7 of A3028M-AA and 1 of A3028M-AAA, our first epoxy-encapsulated dual-channel 0.3-640 Hz transmitter. Frequency response is N151_5mV within ±0.4 dB for the M versions. Variation in the absolute gain is due to variation in battery voltage of the freshly-inserted batteries. We place all the transmitters in their bags, turned on, and within a larger bag, and then in hot water and measure noise. Total noise is ≤12 μV in the Ns, and ≤14 μV in the Ms. Switching noise is ≤3 μV.

[17-FEB-17] We have batch B152 consisting of five A3028B-DC. Frequency response B152_5mV within ±0.2 dBm. Switching noise in B152.2 is 6 μV with total noise 16 μV. We reject this one. The other four have switching noise 4 μV or less, total noise 12 μV or less. We have two prototype transmitters, Q154.22, Q154.39 are equipped with the CR-2354/HFN 560 mAhr battery. Switching noise ≤1 μV, total noise 5 μV. Volume is 5.0 ml. Frequency response also in B152_5mV. We have Q154.56 and Q154.73 made with the CR-2450/H1AN battery 620 mAhr. Switching noise also ≤1 μV, total noise 5 μV. Volume 5.5 ml. Frequency response in B152_5mV.

Poaching transmitters C111.3, B146.8, B146.9, B129.12 all turn on and give 100% reception, a one-second interval shows the corrosion artifact in their signals here. B129.12 still functions well enough to record EEG, but its gain is 10 dB too low. We turn them off again and put them back in the oven, but now at 80°C. We put Q154.56 and Q154.73 in to poach at 80°C. We add E144.10 and E150.6, both of which have excessive switching noise.

[22-FEB-17] Poaching transmitters B146.8, B146.9, B129.12 all turn on and give 100% reception. C111.3 won't turn on and we see brown corrosion beneath the silicone around the positive battery tab. Q154.56, Q154.73, E144.10, and E150.6 RF spectrum centered on 900 MHz when first removed from oven at 80°C, and reception with A3027E is 80%. After a few minutes to cool down, 100% reception and correct gain versus frequency for 50-Ω sweep.

[27-FEB-17] Poaching transmitters B146.8, B146.9, B129.12 all turn on and give 100% reception. All three generate a 0.5-Hz full-range square wave. Q154.56, Q154.73, E144.10, and E150.6 reception is 100% after after a few minutes to cool down. Gain versus frequency for 50-Ω sweep is correct.

[28-FEB-17] Poaching transmitters B146.8, B146.9, B129.12 all turn on and give 100% reception. Q154.56, Q154.73, E144.10, and E150.6 reception is 100% after after a few minutes to cool down. Gain versus frequency for 50-Ω sweep is correct in Q154.73, E144.10, and E150.6, but 6 dB too low in Q154.56. Gain versus frequency for 10-MΩ source is too low for all sources at 100 Hz, see here.

MAR-17

[03-MAR-17] Newly-made transmitter E152.13 active current 120 mA after encapsulation in epoxy, before silicone coating, using the multimeter's milliamp range. It has drained its battery. Poaching transmitters Q154.73 gain is 6 dB too low at 100 Hz with 50-Ω source. Q154.56 gain 6 dB too high at 100 Hz. E150.6 gain 1 dB too low at 100 Hz. E144.10 gain normal. Noise &leg;12 μV after allowing to settle. B129.12 gain 10 dB too low at 100 Hz. B146.8 gain 20 dB too low at 100 Hz, B146.9 no gain at 100 Hz, produces 0.5-Hz square wave. Newly-made transmitter E153.11 drains its battery after clipping the extension and loading battery. We disconnect the battery. Active current is 115 mA with the milliamp range and 300 mA with the ampere range. Component U9 is hot. We replace and active current consumption is 78.1 mA. We go back to E152.13, burn off epoxy around U9 and apply power. U9 heats up. We remove U9. Active current is now 41 μA. Before failure, with U9 loaded, active current was 80 μA. We believe U9 is being damaged by shorting A to 0V while loading the battery.

We have batch E155 consisting of fourteen transmitters including some with channel numbers greater than 14. We are sanding down the lump of epoxy that forms over the circuit board during encapsulation on the rotator. Each transmitter has a flat-topped look to it. We find one bubble in silicone that we feel must be filled. One device has been sanded to the point where we can see the tops of two ICs, half of them to the point where we can see one. Frequency response E155_5mV within ±0.5 dB. Total noise 1-250 Hz ≤12 μV for half-second intervals. Switching noise in 37°C water ≤5 μV.

We receive back from Marburg five transmitters that failed prematurely. During e-mail discussions of these failures, we came to some tentative conclusions. "R106.7: Was running while on shelf, exhausted most of its battery before implantation." R106.7 won't turn on. Disconnect battery. Silicone comes away easily, together with enamel coating. VB = 0.5 V. Connect external 2.6 V. Inactive current 1.8 μA, active 83 μA. Reception 100%. Response to 50-Ω sweep correct. With 255 mA-hr battery, operating life should be 128 days.

"R115.1: Broken EEG lead." R115.1 won't turn on. Antenna has been pulled away from the EEG leads and is exposed at the tip. Silicone hard to remove and in perfect condition. Rotator-made epoxy. Epoxy so thin around XYC corner that we can see two capacitors and a resistor. VB = 0.3 V. Connect external 2.6 V. Inactive 1.8 μV, active 82 μV. Reception 100%. Attach external battery. Gain with 20-MΩ sweep is correct. Noise with leads in water 15 μV. Noise with leads and antenna tip in water 400 μV. We compare the spectrum of the noise with and without the antenna tip in the water with the spectra below.

Figure: Spectrum of Noise from R115.1 With EEG Leads In Water and Antenna Tip Outside (Left 0.8 μV/div) and Inside (Right 8 μV/div) Water. Note that the vertical scale is ten time greater on the right, in which the fundamental of the switching noise is 60-μV in amplitude. For the appearance of the signal itself see Breached Antenna Noise.

The noise we see with the antenna tip in the water is exactly the noise we see on a currently-implanted transmitter at Marburg, R121.4. This noise has the same spectrum as the noise generated by our hall-effect magnetic sensor, which we call "switching noise". The amplitude of the fundamental component of the switching noise is 60 μV. When we remove the antenna from the water, this amplitude drops to less than 1 μV. We conclude that R117.14 and R115.1 both suffered from noise generated by damaged antenna insulation.

R110.4 we suspect was left running on the shelf before implantation. It failed 80 days after implantation. The device does not turn on. Disconnect battery. Silicone in good condition. Some enamel pulls off. VB = 0.8 V. Connect external 2.6 V. Inactive 1.7 μA, active 83 μA, 100% reception. Gain with 50-Ω sweep is correct. Noise with leads in water 16 μV. With antenna in the same water, noise is 500 μV, with switching noise 120 μV.

R112.6 was implanted immediately upon arrival and failed after 118 days. Antenna has been pulled away from EEG leads. Will not turn on. Disconnect battery. Silicone in good condition. VB = 0.8 V. Connect external 2.6 V. Inactive 1.8 μA. Active 84 μA. Noise with leads in water 15 μV. With antenna in same water, insulation intact, 15 μV. With insulation removed from tip, switching noise is 120 μV. With a 255 mA-hr battery and 84 μA operating current, we expect this transmitter to run for 126 days. It failed after 118 days implanted and a one-day burn-in for 119 days total, which is consistent with battery capacity 240 mA-hr.

We take transmitter B152.2, which failed quality control because of switching noise 6 μV. We immerse in hot water and observe switching noise of 8 μV. We pull the antenna away from the EEG leads and put just the EEG leads in water. Switching noise is now 3 μV. E116.10 when immersed in water shows 4 μV switching noise. We immerse only the leads. Switching noise 5 μV. Pull antenna away from EEG leads. Switching noise 5 μV. Arrange antenna to be far from the leads. Switching noise 3 μV. C143.14 has switching noise 16 μV immersed warm water. We place only the leads in water, 12 μV. Pull antenna away from leads, immerse leads in water, 10 μV. Although the antenna is a potential source of switching noise, it is not the only source, nor even the main source for switching noise arising after encapsulation.

[17-MAR-17] We have batch E154 encapsulated in epoxy on the rotator, sanded flat on top side, coated once with SS-5001, except E154.1 and E153.14, which are coated twice with EE-6001. We measure frequency response E154_5mV within ±0.4 dB. Noise in water at 37°C is ≤13 μV with switching noise ≤4 μV. Silicone coating shows no cavities except for E154.7, which has a 0.5-mm diameter cavity beneath the surface. We take E154.7 and E154.1 to poach.

Poaching transmitters B146.8 and B146.9 will not turn on. Dissect B146.8. Battery 0.3 V. Disconnect 0.3 V. Apply external 2.6 V. Inactive 6 μA at first, dropping to 3 μA, active 90-200 μA fluctuating. Diagnosis "corroded capacitor". B146.9 battery 0.1 V, disconnect 0.1 V. Apply external 2.6 V. Inactive 15 μA dropping to 8 μA. Active 150-2000 μA fluctuating. Diagnosis "corroded capacitor". B129.12 turns on and generates 0.5-Hz oscillation. Q154.56 and Q154.73 are both off. We suspected they were both off last time we checked them, and so were careful to make sure they were on when we put them in the oven and we had no magnet near them when we removed them from the oven. They both turn on and we get 100% reception, gain 20 dB too low at 100 Hz. E150.6 gain 10 db too low at 100 Hz with 50-Ω source and VA = 2.1 V. E144.10 gain normal with 50-Ω source and VA = 2.3 V. Add E154.7 and E154.1.

[20-MAR-17] Poaching transmitters E154.1 and E154.7 100% reception gain normal with 50-Ω source and 20-MΩ source. B119.12 100% reception, no oscillation, gain 20 dB too low at 100 Hz. Q154.56 and Q154.73 are both off. We turn on Q154.73. VA = 3.1 V. Noise 11 μV, gain 20 dB too low at 100 Hz. Q154.56 will stay on only if we leave the magnet resting on the device. It generates a 1-Hz square wave. After a few minutes, it turns off and we cannot turn it on again. E150.6 won't turn on. E144.10 will turn on only if we rest the magnet on the device, and generates 0.3-Hz square wave. We remove !154.56, Q154.73, E150.6 and E144.10 from poach and will dissect tomorrow.

[29-MAR-17] Poaching transmitter E154.1 100% reception, gain normal for 50-Ω and 100-kΩ sweeps, 14 dB too low at 100 Hz for 20-MΩ sweep, VA = 2.77 V. E154.7 100% reception, gain normal for 50-Ω and 20-MΩ sweeps, VA = 2.80 V. B129.12 will not turn on after 64 days at 60°C and 40 days at 80°C. This poach is equivalent to a total of 10×64 + 60×40 = 3040 days at 37°C.

Figure: Corrosion Beneath Silicone in B129.12. We see white tendrils of some new substance spreading out from the edge of the circuit board, where it is not covered with epoxy. We see brown corrosion at the clipped edge of the circuit board.

The corrosion around the edges of the circuit board suggest that our epoxy coating is too thin on the edges to remain intact when poaching.

We have batch B201_17 consisting of twelve A3028B-AA transmitters with channel numbers in the range 17-33. Gain versus frequency B201_17 within ±0.4 dB. Total noise ≤16 μV except for B201.18 and B201.28 which are 18 μV. Switching noise ≤6 μV except B201.18 and B201.28, which are 8 μV. We reject B201.18 and B201.28 and set them aside for dissection.

[13-APR-17] Poaching transmitter E153.7 100% reception. E154.1 has stopped. This device has two coats of SS-6001. The silicone has a yellow shade where it is thick, and around the base and tip of the antenna. We bend the base of the leads and the antenna tip pops out of the silicone.

Figure: Discoloration and Cracking of SS-6001 After 27 Days Poaching at 80°C.

We dissect E154.1. VB = 1.0 V. Disconnect VB = 2.2 V. Connect external 2.7V, inactive 2.0 μA, active 1.8 mA. Reception 100%, transmitting all zeros. We remove C5, C2, and C6 but 1.8 mA persists. But VA = 0.2V which suggests a corrosion resistance between VA and 0V. Diagnosis "unidentified drain". We have E153.14, which also has SS-6001 coating. We place it in the oven to poach, along with R129.6, which has MED10-6607 coating.

[21-APR-17] We have a collection of leads that have soaked in acetone at room temperature for a week with a 20-ml lump of dental cement. The acetone is now pink, the color of the dental cement.

Figure: Pink Dental Cement Dissolved in Acetone.

We remove the leads and set them on a piece of paper. After a few minutes they look like this:

Figure: Residue on Leads After Dissolving Dental Cement.

When we wash the jar with water, we get a sudden appearance of a thick white residue.

Figure: Residue on Inside of Jar After Pouring Out Acetone with Dissolved Dental Cement.

We wash the jar with acetone and wipe it out. A surface discoloration remains, but almost all the residue is gone. We shake the leads in clean acetone, remove, and place on paper to dry. A film remains on the leads, disturbing the reflection of light from the lead surface.

Figure: Residue on Leads After One Acetone Wash.

We soak the leads in acetone for ten minutes, shake them well, and wipe them each on a clean lint-free cloth. We now find that their surfaces stick to gether in the same way they do when they are clean and new. The surfaces are shiny. After a few minutes drying, they have no odor. With tweezers we can make no mark in any film on their surface.

Figure: After Second Acetone Wash and Wipe.

We wash with hot water. The lead surfaces are hydrophobic. We see no sign of the white film we created earlier with water washing in the jar. We conclude that the leads are clean.

We have been poaching our selection of silicone leads, after their experiences with acetone and dental cement, for the past four days in water at 80°C. We examine them today. They are clean, shiny and flexible.

We have batch E200_39 consisting of fourteen transmitters. Each has one coat of SS-5001 and an outer coat of MED10-6607. Most of the leads have a squashed point where they were held in spring clamps during dipping. We check all transmitters for breach of insulation at these points and find no breaches. We turn them on and let them run in hot water for an hour. We refresh the water at 37°C. Switching noise ≤5 μV, total noise is ≤13 μV. Gain E200_39 within ±0.4 dBm.

[19-MAY-17] Poaching transmiters: R129.6 100.0%, 2.51 V, 15.7 μV. Gain 20 dB too low at 100 Hz. R153.14 has stopped. We able to turn it on again and it generates a 1-Hz square wave with 100% reception. Dissect. Silicone is yellow and well-adhered to epoxy. Battery voltage 2.9 V. Disconnect, battery voltage 3.0 V. Connect external 2.7 V. Inactive 2.5 μA, active 95-105 μA varying with the square wave. After two minutes, the transmitter turns itself off and inactive current is 2.1 μA. We cannot turn it on again for a few minutes. Now active current is 900 μA for a while, then it turns off. Diagnosis "Corroded Capacitor".

[14-JUN-17] Poaching transmitters. E146.2 100% reception, generating its own square wave when open circuit and in water. Top layer of silicone is coming un-stuck. E154.3 and E155.21 won't turn on. Top layer of silicone coming un-stuck.

We assemble our first three A3028V-CAC dual-channel EEG/EMG transmitters. Channel X is 0.3-160 Hz, 512 SPS. Channel Y is 30-640 Hz, 16 SPS. We have replaced C12 with 1.0 nF and C14-C16 with 240 pF. We apply a frequency sweep and measure gain versus frequency by looking at the amplitude of the samples we receive.

In the third plot, we connect X to C and apply the sweep to Y while measuring the signal on X. There is no significant cross-talk between the EMG input and the EEG input within the circuit. When we leave all three leads open circuit in air, however, we see the following transmitter-generated noise of amplitude 18 μV.

[21-JUL-17] We have batch M203.17-51, all A3028M-AAA. Frequency response M203_17 and M203_17_More within ±0.35 dB except for M203.51, for which Y gain is 2 dB too low. Noise ≤16 μV in 0.3-640 Hz bandwidth. We observe an intermittent 1-μV peak around 20 Hz in one transmitter, but no sign of swithing noise in any others.

AUG-17

[01-AUG-17] Poaching transmitters E201.57 and E201.61 have stopped.

[04-AUG-17] We have batch E201_113 consisting of fourteen A3028E-AA. Frequency response E201_113 lies within ±0.9 dB, the greatest variation occurring at 130 Hz. Switching noise in 37°C water is <4 μV, total noise ≤12 μV rms except for E201_119, which shows 5 μV and 15 μV respectively. One of them E201_114 has a blue lead 20 mm too short. We keep this one to poach.

We have batch B202_39 consisting of four A3028B-AA. Switching noise in 37°C water <3 μV and noise <10 μV rms. Frequency response E202_39.

[15-AUG-17] Dissect E201.57. Outer layer of MED-6607 well-adhered to main coat of SS-5001 and still flexible. We peel most of it off then cut away the SS-5001. VB=1.1 V. Disconnect, VB rises to 2.2 V in one minute. Connect external 2.7 V. Inactive 5 μA, active 1.6 mA dropping occasionally to 90 μA with 100% reception. But after two minutes, rises to 2 mA and no reception, cannot turn off. Burn epoxy away from C2 and C5, connect new battery, get 100% reception, gain with 50-Ω source is 20 dB too low, and we see steps in average value. Diagnosis: Corroded Capacitor.

[16-AUG-17] We receive recorings from ION/UCL of the last two days of C143.5, 14-AUG-17 after 33 days implanted. This device we shipped 26-NOV-16, so it has been consuming 2.5 μA for 200 days before consuming 50 μA for 33 days, a total of 52 mA-hr from its nominally 48 mA-hr battery.

SEP-17

[05-SEP-17] We have batch E201_129 consisting of sixteen A3028E-AA. Encapsulated with one coat of SS5005 and one coat MED-6607. Switching noise in 37°C water is ≤4 μV except E201.140 with 5 μV. Total noise is ≤14 μV for all. Frequency response E201_129 within ±0.7 dB.

Poaching transmitter E201.114 reception 100%. Noise 10 μV until place in cold water, then 0.5-Hz oscillations start. We leave the transmitter at room temperature for three hours. It turns itself off. We turn it on again and it oscillates as before.

We have our first transmitters equipped with rechargeable LiPo batteries. All transmit at 512 SPS and 0.3-160 Hz. No1 and No3 have 19-mAhr batteries, No5 has a 190-mAhr battery. We place in warm water. Noise is 4.2 μV, 4.5 μV, and 5.3 μV respectively. Switching noise is 0 μV, 0.7 μV, and 0 μV respectively as viewed with a 32-s interval. Volume of No1 and No3 combined is 3 ml, making each 1.5 ml, slightly more than our A3028B with its 48-mAhr primary lithium cell. Volume of No5 is 6 ml, a little less than our A3028L with its 1000-mAhr primary lithium cell. Looking at the smaller encapsulations, we may have to add more material to round off the corners of the battery pack. Looking at the larger encapsulation, we could use less epoxy and silicone. To the first approximation, the battery capacity per unit volume is 30% of the primary cells devices.

[11-SEP-17] Poaching transmitters with LiPo batteries gain versus frequency normal for 100-kΩ sweep. Total input noise ≤6 μV. VA = 3.76, 3.73, and 4.91 V for No1, No3, and No5. The small No1 and No2 appear unaffected by poach. But No5 looks larger. But we measure its volume to be 6 ml as before. We smell a hint of the sweet odor we associate with old or exhausted LiPo batteries.

[12-SEP-17] Poaching transmitter No5 with the large battery has burst its silicone. The battery is puffed up. It is not running, but when we turn it on, it powers up just fine and we get 100% reception. The other two also give 100% reception, and look unaffected.

We cannot recharge the battery through the EEG leads in this mock-up, but the form and battery life will be identical to that of the proposed A3028E-R.

OCT-17

[03-OCT-17] We have the above A3028E-R prototype encapsulated in epoxy and silicone, call it ER.8. Dip in epoxy with thirty second run-off and rotate to cure. Repeat. Paint exposed parts with epoxy. Cover corners with SS-5001 silicone. Dip three times in MED-6607. Maximum dimensions 32 mm × 22 mm × 9 mm. Displaces volume 4.0 ml. We test then put in the oven at 60°C to poach.

[06-OCT-17] We solder two stainless steel, teflon-insulated wires to a BR1225 coin cell. We need acid flux to solder to the surface. We can apply a solder blob immediately. We let the iron sit on the battery surface for ten seconds. The battery is too hot to touch. We wash in water and attach to an A3028U consuming 150 μA. Battery voltage is 2.5 V. We leave it running.

Poaching transmitter ER.8 battery voltage 3.86 V, reception 100%. Response to 100 kΩ sweep correct. No sign of swelling in ER.8 nor in another non-functioning A3030E we started poaching at the same time.

[10-OCT-17] Poaching transmitter ER.8 battery voltage 3.83 V, reception 100%, response to 100 kΩ sweep correct. No sign of sweeling in ER.8 or A3030E dummy, but both devices have a faint sweet smell, as does the poaching water. Our 150-μA transmitter equipped with over-heated BR1225 is still running with battery voltage 2.6 V.

[13-OCT-17] Poaching transmitter ER.8 battery voltage 3.79 V, reception 100%, response to 100 kΩ sweep correct. Faint sweet smell persists but no bulging of battery. Our 150-μA transmitter equipped with over-heated BR1225 is still running with battery voltage 2.6 V. We have a dummy A3028P pup-sized transmitter made with a BR1225 cell, rotated epoxy, silicone on bumps, three coats of MED-6607. Volume 0.8±0.2 ml, length 21 mm, width 13 mm, and height 4.3 mm. With the BR1025 the width will be 11 mm and length 19 mm. With rounded-corner circuit board we can skip silicone on bumbs and apply only two coats of MED-6607 to reduce height to 4.0 mm.

We suspend an A3028RV3 circuit board over a piece of paper 150 mm from a spectrometer loop antenna. With a 50-mm wire we get −34 dBm. With no antenna we get −62 dBm. With the transmitter off we get −67 dBm at the peak of the spectrum. An A3028A in water at same range gives −37 dBm. We load a 63 mm unstretched helical lead and get −45 dBm in air. We cut back the antenna and measure power received in air and water held in a 50-ml beaker. When in water, the antenna tip is in contact with the water.

Figure: Power Received from Helical Antenna. Same antenna base position and line, but length varies. In water, we have the antenna tip in contact with the water and isolated from the water with hot glue.

We repeat, using hot glue to insulate the end of the antenna each time we cut it shorter. An insulated helical antenna, made with the same spring as our EEG leads, works poorly in water when 25 mm long, but very well when 15 mm long.

[23-OCT-17] ML621 voltage 1.85 V with DVM, not receiving from 35-μA transmitter. The ML621 powered the transmitter for around 120 hours, but we expect 170 hours. We suspect that our re-charge was insufficient after the first drain. We plug into 2.9V with 400 Ω in series to re-charge. Our ML920S battery still running our 150-μA transmitter, reporting VA = 1.91 V. With DVM we measure 1.89 V. The device has run for around 70 hours, and we expect 70 hours. Poaching ER.8 battery voltage 3.75 V, noise 6 μV rms, reception 100%, correct response to 100-kΩ sweep. No sign of swelling. Feint sweet smell when held to nose.

[30-OCT-17] ML621 voltage 2.33 V with DVM, 35-μA transmitter not running at first. We plug the battery back in and it powers up with VA = 2.25 V. Runs for about ten minutes befor switching off with low battery voltage. The ML621 ran for at most 140 hours when we expect 170 hours. The SL-920S voltage is 1.4 V with DVM, 150-μA transmitter not running. Recharge with 2.9 V through 400 Ω. ER.8 reception 100%, noise 5 μV rms, response to 100-kΩ sweep correct. No swelling.

We have eight A3028U-DDK from batch U201.151. We measure volume of all eight by water displacement to be 11 ml, individual volume is 1.4 ml.

NOV-17

[03-NOV-17] We record the battery voltages reported by our 35-μA and 150-μA transmitters when powered by fmanganese-lithium batteries ML621 and ML920S respectively after charging both with 2.9 V through 400 Ω.

Figure: Manganese-Lithium Battery Discharge. We use the average value of X to measure VBAT. The ML621 is discharges at 35 μA. The ML920S discharges at 150 μA through a two-channel transmitter.

The ML621 provides 1.4 mA-hr, far less than its nominal 5.8 mA-hr. The ML920S provides 7.6 mA-hr, less than its rated 11 mA-hr. We find the following re-charge curve, which suggests we should be charging with 3.1 V. Judging by this curve, it looks like 30% of the re-charge energy is delivered above 2.9 V. We charge our ML621 and ML920S with 3.1 V through 400 Ω for 24 hours each.

We have batch U201.147-171 consisting of 12 A3028U-DDB. Our LWDAQ function generator has a DC offset that we remove with a 1-μF capacitor. We connect a 50-Ω 33-mV sweep through the capacitor to each input in turn and measure frequency response from 0.25 Hz to 1000 Hz. We obtain U201_147 within ±0.8 dB. When we place the devices in water, many of them are excessively noisy on either X or Y, but not both. We remove from water and place on foam pad in faraday enclosure. Noise in 2-160 Hz is 35-40 μV rms, or 8 counts rms. Switching noise observable in 8-s intervals is ≤6 μV. Because we still see switching noise, despite the gain being ×10 rather than ×100, the switching noise cannot be introduced at the EEG input. If it is not introduced at the EEG input, it cannot be introduced at the input to the second stage of amplification either. So the noise must be getting into the ADC through its power supplies.

ER.8 reception 100%, VA = 3.70 V, response to 100-kΩ sweep correct, noise 5 μV rms. We put U201.161 and 163 in the oven at 60°C to poach. We see full-scale fluctuations on the inputs. In one interval, we see 161 at 811 counts, 162 at 772 counts, 163 at 45775, and 164 at 65528.

[06-NOV-17] We have batch J204.1-23 consisting of 11 of A3028J-CMC encapsulated with epoxy and three coats of MED-6607 only. We have not yet soldered the silver wire onto the Y lead. The volume of all eleven with antennas included is a 14 ml, making their body volume a little less than 1.3 ml. All parts are well-covered by epoxy and silicone with the exception of U9, which is right next to the edge of the printed circuit board, with corners that push out. But the silicone over these corners is still smooth, even though it protrudes, and there is no metal on the corners. All leads ≤0.8 mm diameter. The Y channels have 0.3-80 Hz, X 0.3-160 Hz. Frequency response is J204_1. Noise is ≤10 μV with switching noise &leg;4 μV.

We have batch J204.25-49 consisting of 11 of A3028J-CMC encapsulated with epoxy and three coats of MED-6607 only. Total volume 14 ml for 11 is 1.3 ml each. Frequency response J204_25 correct to ±1 dB. Noise in 37°C water <15 μV rms, switching noise ≤4 μV.

We have B152.5, a transmitter with excessive switching noise. We place in faraday enclosure powered by its own battery and obtain the spectrum on the left, for which total noise 2-160 Hz is 12 μV rms and switching noise fundamental is 8 μV.

With external BR2477 battery, noise 2-160 Hz drops to 5 μV rms and switching noise is less than 0.8 μV. We note that switching noise in transmitters made with LiPo batteries is negligible. We note that the A3028U, with ×10 amplifier, still sees switching noise, which means the noise is arising at the input of the ADC. The BR1225 output impedance is around 44 Ω. Its negative side is pressed against the ADC package on the top side of the board.

[10-NOV-17] Poaching ER.8 silicone in perfect condition, slight sweet smell, no bulging, response to 100-kΩ sweep correct, 6 μV rms noise. U201.161 and U201.163 reception 100%, correct response to 100-kΩ source from 0.1-1000 Hz, noise 40 μV rms in air. In water, average values are 1.2%, 0.5%, 86.7%, and 74.4% of full scale for channels 161 to 164. U201.161 has a 10-mm length of exposed 316SS as its VC electrode and two soldered pins for X and Y. We connect its threee input pins together and put it back in water. Inputs are now 57.8% and 57.6% of full scale. We separate the VC lead. We get 1.1% and 1.5% of full scale. We connect C and Y, leaving X separate. Now X is at 0.0% and Y is at 58.3%. Add salt to water, X = 1.1%, Y = 0.4%. Connect all three together in saltwater we get X = 1.1%, Y = 0.4%. But U201.163 in the same saltwater with leads separated gives X = 82.7% and Y = 83.3%. In air again with leads isolate, U201.161 gives X = 71.2% and Y = 70.4%. In saltwater, separate leads, cut VC lead to 1 mm, X = 1.1%, Y = 0.4%. Solder a stainless steel screw to VC, put back in water X = 1.1%, Y = 0.3%. We place leads in water but transmitter body outside of water and get X = 74.0%, Y = 65.5%. This transmitter we rejected because the support wire pad came off and we used the 0V battery pad for the support wire. We tried but failed to cover this cut-off support wire. Furthermore, there is a breech in the silicone near the wire. We can taste the 1.8-V potential of VC when we put the entire transmitter in our mouth.

Figure: Effect of 100 μF P1206 4-V Capacitor on Switching Noise. Left: without capacitor, total noise 12 μV rms. Right: with capacitor, total noise 8 μV rms. Note attenuition by capacitor of higher harmonics is more dramatic than that of the fundamental.

[13-NOV-17] Our 150-μA transmitter with ML621 battery stopped after 27 hours, or 4.0 mA-hr. When we disconnect from transmitter, battery voltage is 2.3 V. We reconnect and turn on the transmitter. For ten seconds we see 100% reception of two channels. After ten minutes, VB = 0.65 V. We connect to 3.1 V through 400 Ω to recharge. Our ML920 is charged to 3.09 V. We connect to 35-μA transmitter and leave running.

[14-NOV-17] We add J204.45 and J204.49 to our collection of transmitters poaching at 60°C. All poaching transmitters 100% reception, correct response to 100-kΩ sweep. Encapsulation all in good shape.

[15-NOV-17] Our ML621 battery has charged for 48 hours with 3.1 V through 400 Ω. We connect to our 150-μA transmitter. We measure source impedance of various batteries with a known resistor load, either 100 Ω or 1-kΩ. We notice that the output resistance of a fresh battery is greater, so that we might get a voltage of 2.9 V but output resistance double what we see at 2.7 V. Before testing, we exercise the batteries for few minutes with the measurement load.

Figure: Battery Resistance versus Battery Diameter for Various Battery Types. The source resistance is more a function of diameter than it is of thickness.

The BR1225 output resistance is around 140 Ω, while that of the CR1025 is only 70 Ω. The CR2354 resistance is only 10Ω, while the similar diameter BR2477 resistance is 40 Ω.

[17-NOV-17] Our ML621 is discharged. We re-charge with 400 Ω and 3.3 V. We have B205.1-5 equipped with BR1225 batteries ready for encapsulation. We measure switching noise by putting them in a faraday enclosure with their EEG electrodes in water. We turn them all on within a couple of minutes and record. During 550-750 s we had to re-arrange the transmitters because their leads were slipping out of the water.

Figure: Switching Noise from Five Unencapsulated A3028Bs.

During the 0-900 s interval, the average battery voltage dropped from 2.75 V to 2.55 V. The above drop with time is consistent with our observation of a halving of battery resistance as the battery voltage drops by 0.2 V. We have two A3028Qs equipped with CR2354 batteries ready for encapsulation. We turn them on. Switching noise is <1 μV, with no visible fundamental or harmonics on any of the four available input channels.

[29-NOV-17] Poaching transmitters J204.45 and J204.49 have both stopped after 13-15 days. Expected life 15 days. Diagnosis "Full Life". ER.8 still running. We cut the leads off poached U201.161 and weigh on a precise scale: 2.1 g. The three leads and antenna that we cut off weigh 0.2 g.

We have batch B205.1 consisting of five A3028Bs with long, thin leads. Two of them, B205.3 and B205.4, have a poorly-covered stress concentration at the base of the EEG leads, which we will cover with more silicone. Frequency response B205_1. Switching noise in 40°C water ≤6 μV. Total noise ≤12 μV.

[05-DEC-17] Poaching transitter ER.8 no sweet smell, response to 50-Ω and 100-kΩ sweeps is the same and correct. We add A3028G transmitters G201.183 and G201.185 to our poach. G201.185 has its mounting wire sticking out of the silicone on one corner. The silicone cover of the positive battery tap appears to be no more than 100 μm on both. Before poaching, with leads resting on the table, G201.183 and G201.185 weigh 5.746 and 5.781 g respectively.

We measure the mass of four A3028J/U transmitters with their leads and get 2.449 g, 2.467 g, 2.461 g, and 2.474 g. We cut the leads and antenna off one and these weigh 0.260 g. The weight of the transmitter bodies is around 2.2 g.

[15-DEC-17] We have batch E201.211 consisting of seventeen A3028E-AA, coated four times in MED-6607. Gain E201_211 within ±0.4 dB. Gain of E201.212 is 3 dB higher than nominal at 140 Hz. Two lumps on the leads of E211.219. Total noise in 39°C water ≤12 μV. Switching noise <4 μV.

[18-DEC-17] We have batch B206.9 consisting of nine A3028B-AA, coated three times in MED-6607. We measure lead diameters and find them consistent with our new specification 0.7±0.1 mm, with the minimum thickness being 0.6 mm and the maximum 0.79 mm. Mass of transmitter including antenna and leads is 2.37 g with standard deviation 0.03 g. Total noise ≤14 μV in 37°C water, switching noise ≤5.6 μV as shown here. Gain versus frequency A206_9 within ±0.3 dB.

We have 10 of A3028GV1, first article from assembly house, built to S3028F_1 with the red-masked A302801G printed circuit board. Program all ten as A3028J no problems. Inactive current 1.7±0.1 μA compared to 2.1±0.2 μA for the previous thirty A3028RV3 circuits calibrated. The A3028RV3 contains U1, R2, and R1. With the programming extension in place, roughly 0.3 μA would flow through R2, see S3028C_1. In place of U1, the A3028GV1 uses the logic output of U3 as the power switch for the transmitter circuit. Check frequency response of both inputs at 512 SPS from 1-500 Hz, all correct. Load BR1225 batteries, wash, blow dry and bake. Check noise by connecting all three leads with a clip in a Faraday enclosure. Total noise is 7.4 μV rms on average for all twenty amplifiers. Switching noise is 1.5 μV on average within one minute of turning on with fresh battery, with maximum 2.2 μV and minimum 0.9 μV. The second harmonic of switching noise is half the amplitude of the first harmonic, and the third and higher harmonics are too small to see. Compare to switching noise in the first minute for A3028RV3s equipped with the BR1225 here in which noise was 2-11 μV. The A3028GV1 is equipped with a total of 40 μF decoupling on VB (C1, C2, C19, and C20, assuming VB and VD are well-connected through U3) compared to 10 μF on the A3028GV1.

We have 10 of A3028J-AAA made with the A3028GV1 assembly, unmodified to give the 160-Hz bandwidth on X and 80-Hz on Y.

[16-JAN-18] Poaching transmitter G201.183 still running, 100% reception, VB = 2.33 V. Response of channel 183 to 50-Ω sweep correct, for 184 it's 10 dB too low at 100 Hz. Transmitter G20-1.185 has stopped running. We start it again, VB = 2.1 V. Response to 50-Ω sweep of 5 mV is correct. It is 42 days since we started poaching, suppose 185 failed at 41 days, and suppose 183 would fail before tomorrow, or 43 days. Typical operating life for the A3028G is 42 days. These two devices we burned in for one day in the dry oven before poaching, so they delivered their full life. We end our test of both, diagnosis "Full Life". Silicone in perfect condition. Serial number label ink now dark gray rather than black. No corrosion around mounting wire stub. No separation of silicone from epoxy. Minimal corrosion of solder joints on electrode pins.

Our test batch of 10 of A3028J-AAA made with the A3028GV1 assembly have been soaking in water. No sign of rust. Switching noise less than 2 μV for all devices. Turn on and place in oven at 80°C to poach.

[19-JAN-18] Poaching transmitters all running with 100% reception. Response to 50-Ω sweep is correct for all except No13, which reports VA = 1.9V and cannot amplify its input.

[22-JAN-18] Poaching transmitters all running except No3 and No13, which have stopped and won't turn on.

We have batch A206_23 consisting of ten A2038A-DDC. We apply a 6.3-mV sweep A206_23. Switching noise in 37°C water ≤4 μV. Total noise in 2-160 Hz ≤15 μV rms after scrubbing the pins and screws twice, but up to 40 μV before due to rumble.

We have batch B206_75 consisting of ten A3028B-AA. Gain within ±0.3 dB see B206_75. B206.87 has a sharp-edged breech in epoxy on battery rim with inadequate silicone cover. Reject. Total noise in 40°C water is <9 μV. Switching noise <5 μV.

FEB-18

[02-FEB-18] We have C206.102 a delayed member of an earlier batch. Gain versus frequeny matches the rest of the batch and switching noise in 37°C is 4 μV.

[09-FEB-18] We have batch B206_45 consisting of 9 of A3028A-DDC. Volume of five of them we measure in a beaker to be 6 ml, or 1.2 ml each. We measure the volume of a single transmitter by surface reflection with a precision of ±0.05 ml (one drop) and get 1.2 ml. Frequency respose A206_45 within ±0.3 dB. Switching noise in warm water is <4 μV.

[13-FEB-18] We have EEG/EMG recordings from Edinburge. The EEG electrodes are bare wires held in place with screws, one over cortex, one over cerabellum. The EMG electrode is bare wire in muscle with silicone cap screwed back on to secure. In twenty-five hours of recording there is not a single step artifact in the EEG. Here is the spectrum of an ewight-second interval.

Judging by the frequency response, we are guessing that this is an A3028J-AAA. We see switching noise of amplitude 5 μV rms.

[15-FEB-18] We receive M1513090524.ndf from Edinburgh University, a recording made of intercostal muscles using an A3028B. We see heartbeat and respiration.

Figure: Heartbeat and Respiration in 0-20 Hz Portion of Intercostal EMG. Taken from M1513090524.ndf 16-s interval starting at 48 s.

The heartbeat fundamental is at 6.3 Hz, with harmonics at 13 Hz and 19 Hz. Respiration fundamental is at 2.1 Hz with harmonic at 4.2 Hz.

[27-FEB-18] We have first article, 5 pieces, of A3028PV1. Here is the bottom side of the board:

Figure: Bottom Side of A3028PV1 Assembly.

We connect 2.7 V to the circuit and de-activate. Quisecent current fluctuating 0.5 to 1.0 μA. We look at VB and find the following 29-mV pulses with period 260 ms.

Figure: Pulses on VB Due to Magnetic Switch. Pulse period 260 ms.

We put a 1000-μF electrolytic capacitor across VB. After a while we measure a stable current of 0.8 μA. We disconnect the circuit and after a minute the capacitor itself draws 0.0 μA. Inactive current is 0.8 μA. We program with P3028P01 but oscillator U10 is not producing any signal, just 0V, and current is 400 μA. We set up a ring oscillator between TP1 and TP2 and see 131 MHz, current now 6.2 mA. It turns out we should set all inputs to HOLD, including those that we have used as layout bridges to power and ground pads within the BGA footprint. Having done this, active current is 24 μA. We have no RCK. We try a third assembly with the updated firmware and it works fine. With 512 SPS on X, current consumption is 70.4 μA. We re-program as A3028P, 128 SPS, 0.3-40 Hz, and see active current consumption 30 μA. We obtain the following frequency response with a 20-MΩ 5-mV sweep.

Figure: Frequency Response of A3028PV1 Amplifier.

We see a half-power frequency of about 45 Hz, with which we are well-satisfied. At 30 μA, expected operating life with a 30-mAhr CR1025 battery will be 1000 hrs. With 0.8 μA quiescent current, shelf life will be 52 months.

We have batch B200_55 consisting of 11 of A3028B-AA. Frequency response B200_55 within ±0.3 dB. Noise ≤12 μV in all, with some as low as 6 μV rms total noise from 1-160 Hz. Switching noise fundamental amplitude ≤4 μV in 37 °C water.

MAR-18

[06-MAR-18] We place B200.78, 81, and 82 in the oven at 60°C to poach. We check their frequency response first with 20-MΩ sweep, and find it correct. We have B207.3 and 10 with epoxy before dipping in silicone and we find that they don't turn on. They consume 16 mA from an external supply. We observe 1V8 = 0.0 V and VD = 0.2 V. We believe there is a short under the logic chip from 0V to 1V8.

We remove U10, the oscillator, from an A3028PV1 assembly and program. When we turn on power to the logic and amplifiers, current consumption is 15 μA. We program two more complete A3028PV1, but in both cases U10 does not work, and current consumption is 50-100 μA. We attempt to replace U10 on three assemblies, each of which consume 15 μA without U10. We succeed temporarily in some cases, but cleaning and drying eventually reveal a bad joint under the BGA-4 package. We give up. We erase the logic chip on our single working assembly. We reprogram. We repeat. We try OFF for the pull-up setting and find that does not reduce current. We go back to HOLD. The board is still working fine, drawing 30 μA. We now suspect that U10 was broken during assembly.

[09-MAR-18] Poaching transmitters B200.78, 81, and 82 100% reception, response to 20-MΩ sweep correct. We have batch B207_1 consisting of twelve A3028B-AA. Two failed after epoxy encapsulation. We found they consumed 16 mA when active, and trace this drain to the logic chip, which is shorting the 1V8 power supply. Now we have nine left, after burn-in and three-day soak. Frequency response B207_1 within ±0.3 dB. Switching noise in 37°C water ≤3 μV, total noise ≤7 μV rms.

[16-MAR-18] Poaching transmitters B200.78, 81, and 82 100% reception, response to 20-MΩ sweep correct. We have 15 of A3028PV1 from assembly house. We program, calibrate, and test. Thirteen work perfectly. Active current consumption is 32 μA on average. Two have a fault with U10, the BGA-4 oscillator, circuits 0006 and 0015. There is no CK output and current consumption is 200 μA. We see nothing wrong with the way the chips are soldered. Below is bottom side-view of

Figure: X-Ray of U10 BGA-10 from Beneath And To The Side. Arrows show how the balls are flattened where solder joints are formed correctly.

We have batch B205_6 consisting of ten A3028B-DD and three A3028B-AA. Frequency response B205_6.gif within ±0.3 dB. In water at 37°C we see rumble on the DD transmitters, but <6 μV on the AA. After ten minutes, noise on the DD is still 50 μV or more. We scrub all the pins. Now we have noise <8 μV on all DD and noise <6 μV on the AA. Switching noise fundamental is ≤3 μA and second harmonic is ≤1.5 μV. Two have wrinkles in silicone following a failure of our heating system earlier this week. We reject these, leaving sufficient to complete the job. We put B205.9 and B205.13 in the oven to poach at 60°C.

Figure: A Bare Pup Transmitter Circuit. We have not yet attached the leads and antenna, but the 10-mm diameter battery is loaded.

We load batteries onto two non-functioning A3028PV1 circuit boards. We solder the positive terminal directly to the edge of the battery. We connect the negative terminal with a bent copper wire.

[19-MAR-18] All five poaching transmitters 100% reception and correct response to 20-MΩ sweep.

[20-MAR-18] All five poaching transmitters 100% reception and correct response to 20-MΩ sweep.

[21-MAR-18] All five poaching transmitters 100% reception and detect heartbeat.

We receive back from assembly house two A3028PV1 upon which U!0, the oscillator, produces no signal. Of one of the balls under U10-3 were broken off at the chip, we would expect the fault to be affected by pressing on the chip. We tried pressing on the chip but saw no change in current consumption nor a start-up of oscillation. Here is a side x-ray of one of the two U10s provided by our assembly house.

Figure: Bottom-Side X-Ray of Faulty U10 Showing All Balls In Place and Soldered to Circuit Board. The solder joints are on the top side of the balls in this view.

We remove the two oscillators by heating with a solder blob until they come off onto the blob. We place them top down on paper and look at them through a microscope. Ball U10-3 appears to have broken off in both cases, while the other balls are either still adhered to U10 or have come off when liquid. We soak in hot water to remove flux and obtain the following photograph.

Figure: Underside of Two Faulty U10 from A3028PV1. It appears that Ball U10-3 (VDD) has broken off at the package.

We note that U10, when deprived of VDD = 1.8 V is drawing up to 500 μA from U8 through U10-2 (see S3028P. After removing U10, both circuits consume only 15 μA. It is possible that both U10s have been damaged by U8 through U10-2. Subsequent mechanical connection of 1.8V to U10-3 through its broken solder ball does not start oscillation nor reduce current consumption. Broken solder balls like this were a persistent problem with our old BGA-5, as we described in 18DEC13

[27-MAR-18] All five poaching transmitters 100% reception. Response to 20-MΩ sweep is within 1 dB of correct for all but B200.81, which is 3 dB too low at 100 Hz. Response to 100-kΩ sweep is, however, within 1 dB for B200.81. Total noise ≤8 μV for B200.78, B200.81, and B200.82, which have bare wire electrodes, and ≤16 μV for B205.9 and B205.13, which have soldered pins. We remove the soldered pins and expose bare wire. Now the noise is ≤8 μV. The characteristics below give channel number, battery voltage, and noise in 2-160 Hz for a typical eight-second interval.

Battery voltage for the older three transmitters 78, 81, and 82 is 0.1 V lower than for the younger two. The older transmitters have been running for 500 hours. We expect them to run for another 120 hours.

We have batch E206_103 consisting of fifteen A3028E-AA made with A3028RV3 circuits. Response to 20-MΩ sweep E206_103 within ±0.3 dB. Total noise 2-160 Hz in 44°C water is ≤15 μV with switching noise fundamental ≤5 μV. We have batch B207_12 consisting of four A3028B-AA made with A3028GV1 circuits. Response to 20-MΩ sweep B207_12. In 39°C water, total noise 2-160 Hz is ≤10 μV, switching noise fundamental ≤4 μV.

[30-MAR-18] Poaching transmitters B200.78, B200.81, and B200.82 show some activity with low battery voltage when hot, but turn off when they cool down. It has been 580 hrs, which is within 10% of the expected 620 hours. Diagnosis: full life. Poaching transmitters B205.9 and B205.13 response to 20-MΩ sweep correct, 100% reception.

We have two physical prototypes T1 and T2 of the A3028P. Both are equipped with 0.5±0.1 mm leads and an antenna made of a 0.7±0.1 lead.

Figure: A3028P Prototypes.

Prototype T1 has one thick coat of epoxy with no touch-up and three coats of silicone. Its weight is 1.5 g. Its maximum thickness is 5.2 mm, minimum 4.5 mm. Estimated volume 0.9 ml. Prototype T2 has one thin coat of epoxy followed by touch-up and two coats of silicone. Its weight is 1.4 g. Its maximum thickness is 4.6 mm, minimum 3.6. Estimated volume 0.75 ml.

APR-18

[02-APR-18] Poaching transmitters B205.9 and B205.13 response to 20-MΩ sweep correct, 100% reception. Battery voltages around 2.6V. No rumble in signal. Both were off when we took them out of the oven. We may have turned them off on Friday.

[06-APR-18] Poaching transmitters B205.9 and B205.13 100% reception, response to 20-MΩ sweep correct. Battery voltages at 60°C 2.66 V and 2.62 V respectivey. We have batch B200_83 consisting of 22 of A3028B-AA with 45-mm leads. Volume of 9 together is 12 ml, average 1.3 ml. We change our amplifier gain comparison range from 1-130 Hz to 0.25-160 Hz. With this extended range, the amplifiers agree to ±1.3 dB, which is within a 3-dB spread, see B200_83. In water at 37°C total noise in 2-160 Hz is ≤11 μV. Switching noise fundamental ≤4 μV.

Figure: Noise of 22 A3028B-AA In Water at 37°C.

Of the 22, all pass quality control, but if we remove B200_85 and B200_91 we have maximum noise 9 μV and amplifier agreement ±0.9 dB, so we set them aside.

[13-APR-18] Poaching transmitter B205.13 has stopped. We have batch E206_121 consisting of sixteen A3028E-AA. Gain versus frequency within ±0.7 dB in 0.2-160 Hz, see E201_121. We measure volume of bodies plus antennas and 30 mm of leads for 16 transmitters, avearge volume is 3.3±0.1 ml. We measure volume of 4 bodies to be 12 ml, or 3.0 ml each. These transmitters we allowed to drain of epoxy for less time than usual, resulting in more epoxy on the device, increasing their volume by approximately 0.2 ml. Noise in water at 45°C is ≤9 μV with switching noise fundamental ≤3 μV.

[17-APR-18] We put E206.130 in the oven to poach at 60°C. This device transmitted all zeros for a few minutes during quality control, so we rejected it.

We cut back the antenna of an A3028P transmitter from 50 mm to 5 mm, sealing the end after each cut with an acrylic coating. We immerse the transmitter in the same location in the center of a 250-ml beaker of water 25 cm from an A3015C loop antenna. We use our spectrometer to measure power received by the antenna.

Figure: Power Received from A3028P with Helical Antenna. Range 25 cm.

We place the A3028P with 5-mm sealed antenna up against the glass in a beaker of water in our faraday enclosure with one receiving antenna (position A). We obtain 100% at all locations on our ALT platform. Of 30 random locations in the enclosure, we obtain 100% reception in half, >90% in thirteen, and <20% in two. With two receive antennas we obtain 100% reception everywhere. We drop the transmitter in the bottom of the beaker, so it is horizontal (position B). We obtain 100% reception in 19 of 20 locations and 50% in 1 of 20.

We cut off the antenna entirely and seal with silicone. We cut back the 50-mm antenna on another A3028P to 20-mm. We place both transmitters in position A. We place on the ALT platform and move and rotate at random. We obtain 31% reception from the 20-mm antenna and 69% from the 0-mm. We compare an A3028E with 50-mm loop antenna in position B, an A3028P with 0-mm in A and an A3028P with 15-mm in A, recording simultaneously with one antenna. We get 100.0%, 93.7% and 76.5% reception respectively. We cut back the 15-mm antenna to 10 mm and repeat. We get 96% from the A3028E, 88% from the 10-mm and 55% from the 0-mm. We cut back the 10-mm to 5 mm. We get 99.1% from the A3028E, 98.1% from the 5-mm and 61% from the 0-mm.

[20-APR-18] We repeat the above experiment with the same transmitters in the same positions, but the beaker is empty. We get 99.9% from the A3028E, 54.7% from the 5-mm and 0.9% from the 0-mm. We pour water in and repeat. We get 99.9% from A3028E, 98.3% from 5-mm and 61.7% from 0-mm. We load a new 13-mm antenna in place of 0-mm. We try A3028E in water B, A3028P 5-mm in water A and 13-mm outside the wall of the beaker, in air, position C. We have double-coated the 5-mm antenna in acrylic to make sure it's isolated. We get 98.8% from A3028E B, 92.3% from 5-mm A, 92.8% from 13-mm C. We double-coat the 13-mm in silicone and place it in water along with the 5-mm in position A. We get 99.5% from A3028E, 91.7% from 5-mm and 99.0% from the 13-mm. We empty the beaker, leaving A3028E in B and the 5-mm and 13-mm antennas in C. We get 99.9% from A3028E, 61.4% from 5-mm, and 95.1% from 13-mm.

The 13-mm antenna gives us over 90% reception in air, in water, or near water. We connect two antennas inside our enclosure and measure reception from A3028E in water B and 5-mm and 13-mm antennas in water at A. We get 99.9% from A3028E, 99.3% from 5-mm, and 98.0% from 13-mm.

We have batch P1_89 consisting of 11 of A3028P-AA. Frequency response P1_89 within ±0.5 dBm. Noise ≤4 μV in 2-100 Hz. Transmit center frequencies in range 913-918 MHzz. We have three breaches in the silicone, which is too thin. We dry out and add another coat of silicone, making three coats total.

[24-MAY-18] Poaching E206.130, E200.119 response to 20-MΩ sweep correct and 100% reception. P90 100% reception and amplifiers and filters still working, but the baseline signal is swinging around, with bumps a few times a second.

[25-MAY-18] Poaching E206.130, E200.119 response to 20-MΩ sweep correct and 100% reception. P90 100% stops transmitting. We find that its antenna has corroded through at the base under our failed silicone patching. Even the antenna pad has corroded all the way through the circuit board, and the X− lead beside the antenna. Battery voltage 2.2 V. External 2.7 V, inactive 0.8 μA, active 19 μA. Diagnosis, Faulty Encapsulation.

[29-MAY-18] Batch P1_89 consisting of 12 of A3028P-AA now has three coats of silicone. No sign of rust or corrosion after five-day soak. Total noise in 0.5-40 Hz is ≤3.5 μV. No trace of switching noise. Reception 100%. Volume of 10 pieces is 6.0 ml. Mass is 1.41±0.01 g.

JUN-18

[01-JUN-18] We receive 30 of A3028PV1, build B76438. We test 26, 9 work. Of the 17 that fail, 2 have U10 working but consume excessive current (9 mA in No17, 0.11 mA in 07) until we remove U10, ASTMTXK, then current drops to 15 μA. Another 2 have the oscillator frequency varying with time, 4-6 kHz gradually, then fluctuating rapidly (22 and 11). The remaining 13 have U10 generating no signal and consume 30-300 μA. We remove U10 from half of these and current in every case drops to 15 μA. We re-program and feed 32.768 kHz in through TP1 and all these boards work perfectly. Of the 9 that work, 2 end up consuming 85 μA and 95 μA so we remove U10 and reprogram to show that U10 was responsible for the excessive current.

[05-JUN-18] We replace U10 on another 11 of our A3028PV1 circuit boards and all are now working. We cannot replace U10 on 3 boards because the solder mask over the track leading from U10-3 has come off and the exposed coper wicks the U10-3 solder ball all the way to U4-3. We revive two boards from the previous build and they work. We are left with 4 un-touched boards, 2 with fluctuating oscillators, and 23 working. We take a working board and erase the logic chip, but U10 still works. If we drive U10's output with the logic pin, current consumption increases bny 200 μA but U10 works after re-programming. We hear from assembly house, "We suggest running using a LeadFree profile and Leaded solder if they want to continue using this part. Additionally we will place notes for handling glass parts on this board. If this is sufficient then we will need to notify ENG to update paperwork."

[19-JUN-18] We place 5 of A3028P3 bare circuits with fresh batteries soldered to the boards, and 20-mm antennas, in our big faraday enclosure. The A3028P3 runs at 512 SPS and its current consumption is around 75 μA. We expect 400 hrs of operating life. Poaching transmitters E200.119 and E206.130 100% reception, VA = 2.84 and 2.78 V respectively at 60°C. E200.119 response to 20-MΩ sweep correct. E206.130 response to 20-MΩ sweep 20 dB too low, response to 50-Ω sweep correct.

We unpack 3 of our A3028PV1 assemblies. We connect 2.6 V and scrape the solder mask from the track leading between U10 and U8. In 2 circuits we see a 1.8-V, 32.7 kHz square wave. In 1 circuit we see 0 V. We program all three boars. We see 85 μA and 95 μA operating current in the first two boards, with the 32.7 kHz appearing on TP2. We see 29 μA on the third board, with no 32.7 kHz. The nominal operating current is 75 μA. With the oscillator removed we expect 15 μA. These three examples of U10 are consuming 10 μA, 20 μA, and 14 μA.

We receive recording of baseline and picrotoxin seizures from an adult mouse with an A3028P-AA implanted at ION/UCL. Baseline amplitude is 40 μV rms. Seizure spikes 1 mV, see here. Average reception in two hours of recordings is 98% with 97% of intervals having ≥80% reception.

[22-JUN-18] We have batch B202.43 consisting of 9 A3028B-DA. We add B200.85 to make ten. Frequency response B200_43 is within ±0.4 dB. Total noise 2-160 Hz in 37°C water after scrubbing pins is ≤10 μV, switching noise ≤5 μV. But B202.49 shows intermittent steps of several millivolts, even after scrubbing the leads twice and isolating it in its own beaker. We find a strand of antenna wire sticking through the silicone.

[25-JUN-18] We have B204.49 after removing stray wire and coating twice with silicone over the cut end. We place in water at 37°C. We scrub the lead tips. No sign of the intermittent steps we saw earlier. Noise is 10 μV rms 2-160 Hz. Removce from water and place in air. See no rumble. Noise is 9 μV.

We send four ASTMTXK oscillators back to the manufacturer, here they are arranged on a gel back with symptoms listed, as observed when they arrived from assembly house, and a few weeks later.

Figure: Four ASTMTXK for Return. We removed parts with iron at 500°F, washed, wiped dry on microfiber cloth, then placed in gel pack.

The balls are no longer intact on the bottom of each BGA-4, but we make sure each pad has a coating of solder.

[04-JUL-18] We have batch B207_18 consisting of fifteen A3028B-AA. When we have added a drop of silicone to cover the tips of the antenna wires, and in a few cases this drop has a cavity, but the problem is cosmetic only. Frequency response B207_18 with ±0.5 dB. Switching noise in 37°C water ≤3.2 μV, total noise 2-160 Hz ≤8 μV.

Figure: We discharge five CR1025, 30-mAhr, 3-V cells with five A3028P3 transmitters, channel numbers given in legend, each consuming ≈75 μA.

Average battery life it 400 hrs, expected is 400 hrs, range is ±2.5%.

[24-JUL-18] Poaching transmitters 100% reception. We have batch B202.56 consisting of 11 of A3028B-DA. Frequency resposne B202_55 within ±0.7 dB, switching noise in 37°C water ≤3.5 μV, total noise ≤12 μV (there are pins soldered to the lead tips). We can see the red top side of the circuit board at the corners, the epoxy is so thin. But silicone coating is firm.

[07-AUG-18] Poaching transmitters B202.61, B207.30, B207.33, and B207.34 reception 100%, response to 20-MΩ sweep correct. B200.91 active 78 μA, inactive 2.0 μA. Dissect E206.130. Silicone well adhered. No sign of corrosion. VB = 2.8V. Connet external 2.7 V. Active 85 μA, inactive 1.7 μA. Diagnosis "Temporary Shutdown". Repair three of four A3028PV1 circuits by loading SiT1552 for U10. We load a total of four chips and all four work. One we replace because the U10-1 ball was missing, but it worked anyway. The fourth board we could not fix because solder mask is missing from U10-3 to U4 and the track wicks away the ball.

[16-AUG-18] Poaching transmitters B202.61, B207.30, B207.33, and B207.34 reception 100%, response to 20-MΩ sweep correct. A3028P1 transmitter No97 equipped with 0.5-mm wires has been implanted in an adult mouse at ION since 18-JUN-18, but left off. On 30-JUN, 08-AUG, and 09-AUG we turn on the transmitter for a few hours and it records EEG. We receive this report from manufacturer of ASTMTXK oscillator, which we use for U10 in the A3028P devices, showing physical damage to the part around the solder balls, which suggests that the devices were damaged by the pick and place machine. We will have these parts hand-placed in our next assembly job. We receive fine recordings of cortical spreading depressions (CSDs) following seizzures in adult mice using our DC-160 Hz A3028U transmitters.

[21-AUG-18] B207.33 and B207.34 have stopped. We have three A3028T1-R, 0.3-40 Hz with A3028PV1 circuit and ML621 Li-Mn battery 6.8 mm in diameter. We measure battery voltage and get 2.66 V, 2.66 V, and 2.60 V. Looking at our discharge plots, it looks like the batteries are over 90% full. We connect the first one to 3.2 V through 400 Ω and see 400 μA flowing in with 2.92 V across the battery. After a few minutes, disconnect and see battery voltage 2.72 V.

[31-AUG-18] We have batch T209_1 consisting of three A3028T1-R. Frequency response T209_1 correct. Switching noise in 37°C water ≤3 μV, total noise ≤6 μV, see spectrum. Battery voltages 2.55 V, 2.49 V, and 2.46 V. Looking at discharge curves for the ML621 we conclude we must top up the charge of all three devices. We connect T209.1 and T209.2 through 1 kΩ and a microammeter to 4.2 V. Both are turned off. Each draws 130 μA separately, and together they draw 240 μA. If we turn either transitter on, it draws up to 500 μA with full-scaled steps on X. We leave to charge with 4.0 V connected directly to the 1-kΩ charging resistor.

SEP-18

[04-SEP-18] Devices T209.1 and T209.2 have been charging for four days. Current from 4.0 V through 1.0 kΩ is now 6.2 μA. Assuming 3 μA into each device, the charging diodes will each drop 0.45 V, so the voltage on the battery should be around 3.1 V. We place them both in water with T209.3. Battery voltages are 3.24 V, 3.17 V, and 2.41 V respectively. Noise at 25°C is 4.3 and 4.2 μV with switching noise <1 μV. Connect T209.3 to 4.0 V through 1 kΩ and see 90 μA flowing in. Leave to charge up.

[06-SEP-18] Our A3028T1, T209.3 is charged to 3.15 V. We have recorded its charge current with time from a 4.0-V supply through a 1-kΩ resistor.

[11-SEP-18] Our A3028T1 T209.3 battery voltage is 2.14 V. Response to 20-MΩ sweep correct, but we must perform the sweep with a 5-mVpp sweep rather than 10-mV sweep because the dynamic range is now −17…+4 mV. Transmitter has been running for 127 hours.

[19-SEP-18] We place P207.41 and P207.45 in the oven to poach at 60°C. Battery voltages are both 2.96 V. Both are P3028P1-AA, but P207.41 required re-work after epoxy encapsulation, burning away epoxy to re-attach the X+ lead.

[28-SEP-18] We have three A3028T1-R encapsulated with epoxy that fail quality assurance. T209.7 lost its X lead. The other two fail to transmit. The two that fail to transmit both have the same problem: the battery cannot supply 32 μA of operating current. Its voltage drops to 1 V. When supplying the inactive current of 0.8 μA, its voltage is 2.2 V. We connect 3.2 V through 1 kΩ directly to battery T209.6 and see only 7 μA flowing in. Battery T209.11 accepts a 90-μA recharge current. Its battery voltage is 3.1 V. As soon as we disconnect the charging voltage, the battery voltage drops to 2.2 V. We connect 4.0 V through 1 kΩ to the X leads of T209.7 and see 1 mA flowing in.

We take the same ML621 with solder tabs we used for our ML-series recharge experiments. Its votltage is 3.00 V. Apply 500°F iron for ten seconds, clean off flux with water, now 2.92 V. Repeat, voltage 2.86 V. Repeat, and after 9 s the battery voltage drops suddenly to zero. Take out a fresh ML621 from its package. Measure 2.78 V. Apply 500 F and after 10 s the battery voltage drops to 0 V. Apply 500°F for 3 s on, 3 s off, on fourth heating, battery voltage drops to zero. We take a fresh ML621. We load it with 1 kΩ for ten seconds. Its voltage is 2.67 V. We load with 1 kΩ. Voltage drops immediately to 2.49 V, implying output resistance 72 &Omegal;. After one minute, 2.32 V. Disconnect, after five minutes battery has recovered to 2.69 V. Apply 500°F for three seconds, 2.72 V. Apply 1 kΩ, drops to 2.58 V, implying 56 Ω. Apply 500°F for 3 s again, 60 Ω. Apply 500°F for 14 s and voltage goes to 0.00 V. We notice a sweet smell. The plastic ring that separates the terminals has bulged up and out of its slot. The failure is a sudden short-circuit.

Figure: An ML621 With Tabs Soldered to a Blank A302801P Circuit Board. The solder blob on the battery is formed on the cut end of the negative terminal, rather than directly on the battery case. Twenty seconds of heating this solder blob to 500°F fails to heat the battery up to more than 60°C.

Another fresh battery, soldered by tabs to a circuit board, as shown above, has voltage 2.61 V before 1 kΩ load, 2.45 V immedaitely after, for 64 Ω. Short circuit for ten seconds, voltage recovers to 2.45 V after one minute. Apply 500°F to the cut-off battery tab on the 0-V terminal for 20 s, battery voltage stable at 2.58 V.

Figure: BAS116LPH4 Forward Voltage with Current at Various Temperatures. There are two such diodes in the A3028P circuit. We have to extrapolate the 25°C line below 10 μA to estimate the drop at 3 μA.

When we charge the ML621 through the X leads of an A3028T-R, we do so through the 65-Ω resistance of each of its two 27-mm leads, and two BAS116LPH4 diodes. At the end of a re-charge, the current is of order 4 μA. At 25°C, the diodes will each drop 0.5 V. The temperature in our laboratory is, however, closer to 20°C. According to our calculations, the diode voltage should be around 0.52 V, so both of them together are 1.04 V. When we apply 4.0 V, the voltage on the battery will be 4.0 V − 1.04 V − (1120 Ω × 3 μA) = 2.96 V. We have had success charging with 2.9-3.3 V in the past.

OCT-18

[02-OCT-18] Dissect T209.7. Active current consumption with external 2.6 V is 35 μA. Connect batterty. When inactive, voltage is 2.4 V, when active, 2.3 V. We charge battery directly with 3.2 V and 1 kΩ and see 20 μA. We charge with 4.0V and 1 kΩ on the X leads and see 1 μA. There appears to be 1.2 V across D1 with only 1 μA. Something is wrong with internal connections. We connect 20-MΩ 20-Hz 30-mV and see gain varying by a factor of two over the course of seconds. Dissect T209.18. Active 32 μA with external 2.6 V. Battery shows 2.4 V when inactive, dropping to 1.2 V when active. Charge with 3.3 V and 1 kΩ see 20 μA flowing in. Battery is damaged. Dissect T209.13. Active and inactive current 15 mA, no transmission. Battery drained to 1.1 V. Connect 3.3 V through 1 kΩ see 500 μA. After five minutes, disconnect charger and battery is at 2.6 V. Connect to circuit of T209.7 and we see transmission. Battery was drained by excessive current consumption of T209.13, but recovered.

Figure: A3028T-R Discharging. No3 failed QA and we charged it twice for >48 hr through its X leads with 4.0 V and 1.0 kΩ. Later we charged it with 4.2 V. The others are discharging immediately after epoxy encapsulation (AE).

The T209.7 device runs well, but only for 110 hrs after its first re-charge, and only for 75 hrs after its second re-charge. We connect it to 4.2 V to see if we can get it to a full 5 mA-hr. The remaining six discharge curves shown above are consistent with 160-hr operating life, if we accept that No8 and No9 batteries were discharged during assembly and encapsulation.

[05-OCT-18] We have batch P206_171 consisting of 15 A3028P2-AA. Frequency response P206_171 within ±0.8 dB. Noise <5 μV, switching noise <0.5 μV. We identiy our copper spade-end alligator clips as the source of our problems while attempting to charge a set of eight A3028T1-R. We solder gold pins to the leads of one of the devices, but the contact is intermittene between the copper clips and gold or steel. We heated the copper clips with a 650°F soldering iron to assemble them into an eight-position charging fixture, but we see no visible sign of oxide on the surface. And yet the contact resistance varies with pressure and moisture. When measuring the frequency response of batch P206)_171 with these clips, we several times see gain 20 dB too low at 1 Hz rising to correct at 100 Hz, suggesting a contact that resists DC current. We replace all clips with tin-coated steel clips, the same we have been using for years, and all these intermittent problems cease, but we are left with the difficulty of grasping the 2-mil diameter stainless steel wire with such a clip.

[08-OCT-18] Poaching transmitters 100% reception. P207.45 VA = 3.0 V at 60°C, correct response to 1-200 Hz 20 MΩ sweep. P207.41 wandering baseline. Of the eight A3028T1-R we left charging over the weekend, 6 have charge current around 10 μA and two appear to have become disconnected. The 6 have VA 2.9-3.2 V when we turn them on. The 2 have VA = 2.5 V. We re-connect the 2 and see 40 μA flowing into each. We leave them charging. The 6 we leave to run in enclosure.

[09-OCT-18] We have batch Q206_190 consisting of 7 of A3028Q-DNA. We measure the thickness of the epoxy encapsulation and obtain an average value of 9.61 mm, and after one coat of SS-5001 and one coat of MED-6607 we get 11.24. So the silicone coat has thickness 0.82 mm. Frequency response Q206_193 within ±0.7 dB over 0.25-350 Hz, noise 2.0-320 Hz ≤10 μV, switching noise <0.5 μV. We see no switching noise peak in any channel. Poaching transmitters 100% reception.

[10-OCT-18] Poaching transmitters 100% reception. We examine the discharge curves for eight A3028T1-R we finished recharging two days ago, see here. Included in the plot are three discharges of the No3 device. The 72-hr discharge followed a recharge with 4V and copper clips, 112-hr followed 4V and steel clips, 116-hr followed 4.2V and steel clips. We are using only steel clips now. No4, 5, 10, 12, 14, 17 charged up to 2.9-3.3 V with 4.2V and subsequently their discharge remains above 2.5 V for 20 hours. No8, 9 charge to only 2.6V, even though their final charging current is 50 μA each. Their voltage does not rise farther. During discharge, they drop below 2.4V in ten hours. We reject No 8 and No9. We suspect they were damaged during assembly. We leave them to discharge further, and remove the other six, turn them off, and connect them to our group charger. Total charging current is 800 μA.

[19-OCT-18] Poaching transmitters P207.45 and B206.193 battery voltages 2.76 V and 2.70 V. Reception 100%, response to 20-MΩ sweep correct. We have batch C210.1 consisting of 12 of A3028C-AA. Frequency response C201_1. Switching noise in water at 41°C is ≤8 μV and total noise 2-80 Hz is ≤10 μV rms except for C210.7, which is 15 μV rms. The noise on C210.7 does not appear to be switching noise: there is no definite peak in the spectrum. But the noise consists of random 40-μV negative pulses. We add C206.157 (an older batch) and C210.7 to our poaching devices.

We have two sizes of Ag/AgCl electrode we purchased from A-M Systems. One is a 4-mm diameter 1-mm thick AgCl pellet with 70 mm of silver wire. The other is a 3-mm long 0.8-mm diameter AgCl pellet with 70 mm of silver wire. We solder the leads of an A3028Q transmitter as shown below.

Figure: Ag/AgCl Electrodes Soldered to Stainless Steel Leads.

We place the solder joints, silver wires, and pellets in room-temperature water. Input noise for 8-s intervals is typically 5 μV rms in 2-80 Hz. But we see movements below 2 Hz that are up to 200 μV, despite our 0.3-Hz high-pass filter.

Figure: Two Examples of Noise With Solder Joints and Ag/AgCl Electrodes In Water.

We raise the solder joints out of the water leaving only the Ag/AgCl electrodes immersed. While the water is still rocking in the beaker, we see 2 Hz waves. When the water is still, noise in 2-160 Hz is 4.0 μV rms. Variation at lower frequencies is less than 2 μV. The following is typical of all intervals we record from water with two Ag/AgCl electrodes.

Figure: Noise With Only Ag/AgCl Electrodes In Water.

If we allow the solder joints to sit just outside the water, but partly wet, we see occasional steps of up to 20 mV on the input, which appear in the A3028Q signal as a step followed by a decay and overshoot with time constant roughly 0.5 s. We cut off one of the solder joints and strip the end of the stainless steel helix. We place the steel wire in the water along with the smaller pellet electrode to act as a reference on X&minusl;. We see movements below 2 Hz of much the same size and character as when we had the two solder joints immersed.

We continue our experiments with silver chloride electrodes. We first check our Ag/AgCl and 316SS electrode pair in water, and we see the same 200-μV rumble and steps we observed before. This time we take one Ag/AgCl electrode, which is an AgCl-coated pellet connected to a silver wire, and for the second electrode we provide another silver wire. Noise in 2-160 Hz is 3.8 μV and we see no rumble or steps. We cut off the Ag/AgCl pellet, leaving two silver wires in water. We see no rumble or steps. We immerse the newer solder joint in the water along with the new silver wire and see sustained pulses and rumble.

[23-OCT-18] We have three A3028T-R, T19-T21 made for poaching. These are made with the ML621 with tabs, so there is no over-heating of the battery during assembly. Their sample rate is 128 SPS but frequency response is 0.3-160 Hz. Mass of three is 3.04 g. Volume of all three is 1.45 ml. So mass of each is 1.0 g and 0.48 ml, consistent with our current 1.0 g and 0.50 ml specification. Response to 20-MΩ 60 Hz shows beats we expect from under-sampling. Connect to charger along with T209.3 and T209.5. Total charge current 620 μA.

We prepare 200 ml of 1% saline and immerse our two silver wires, attached to A3028Q No39, but with solder joints out of the water. We see 3.9 μV rms noise in 2-80 Hz. Rumble is less than 20 μV in 8-s intervals and there are no steps. We drop the entire transmitter in the saltwater, seal the jar, and place in our oven at 60°C.

[25-OCT-18] Our five charging A3028T-R are consuming 53.5 μA. We remove them one by one. The final charge currents are 30 μA for T209.5, 3 μA for T21, 11 μA for T209.3, 4.5 μA for T20, and 5.4 μA for T19. We turn them all on and put them in our FE3AS to run their batteries down. Poaching transmitters B206.193, C206.157, and C210.7 reception 100%.

[30-OCT-18] Poaching transmitters B206.193, C206.157, and C210.7 reception 100%, response to 20-MΩ sweep correct. After a week in saltwater at 60°C, our A3028Q's silver wires are untarnished, but our solder joints are covered with black and gray residue. We test our two silver wires with their tips in the 1% saline. We see rumble of order 100 μV in each 8-s interval, of which here is a typical example. We solder a new silver wire with an AgCl pellet on the end to our blue lead. Rumble <20 μV in 8-s intervals, no steps. Cut off AgCl pellet leaving fresh silver wire on the blue lead and old silver wire on the red lead. We see rumble up to 100 μV in each 8-s interval, no steps, a typical interval here. We solder an AgCl pellet to the end of our old silver wire. Now we have a new AgCl pellet and a new silver wire in the saltwater. We see rumble up to 100 μV, typical interval here. Even after twenty minutes we are still seeing rumble up to 200 μV, but no steps.

Figure: A3028T-R Discharging. Solid lines are run one, dashed lines are run two. T19-21 batteries with tabs soldered to circuit board, these are their first and second discharges. T209.3 and T209.5 without tabs, soldered directly to circuit board and a wire. These are the fifth and sixth discharges for T209.3, and the third and fourth discharges of T209.5.

The above plot suggests that soldering directly to a ML621 manganese-lithium battery reduces both the operating voltage and the capacity of the battery. We connect all five batteries to our charger. Total current 900 μA. Poaching transmitters B206.193, C206.157, and C210.7 reception 100%, now joined by E210.25.

[05-NOV-18] Our five A3028T1-R have been charging for 60 hours. Total charge current is now 88 μA, down from 900 μA at start. Individual charge currents are T209.3 30 μA, T209.5 27 μA, T19 11 μA, T20 11 μA, T21 9 μA. The final charge current of a healthy ML621 is ≈10 μA. The current passes through two BAS116LPH4 diodes. Their combined voltage drop will be 1.1 V. With 4.2-V charging voltage, the voltage across the 1 kΩ resistor and battery combined will be 3.1 V. [We later discover that our charging voltage is only 4.1 V when the power supply meter shows 4.2 V, so charge voltage this time was 4.1 V.] We turn on all five transmitters and put them back in our cage. Poaching transmitters B206.193, C206.157, C210.7, and E210.25 100% reception, response to 20-MΩ sweep correct. Channel number, battery voltage (V) and noise (μV rms 2-160 Hz) are: 7 2.71 7.1 25 2.69 14.6 157 2.68 7.9 193 2.52 6.2.

[12-NOV-18] Poaching transmitters C210.7, and E210.25, C206.157, 100% reception, VA = 2.72 V, 2.81 V, and 2.63 V. Our five A3028T1-R have discharged their batteries. T21 is still running, but battery voltage is 2.28 V. We connect 19-21 to our charger. The devices are initially active when we connect charging voltage, so we turn them off. Total charge current 650 μA.

[13-NOV-18] Three charging A30238T-R drawing 110 μA today. Poaching transmitters C210.7, and E210.25, C206.157, 100% reception, response to 20-MΩ sweep correct. We have an A3028U DC-160 Hz transmitter and a beaker of 1% saline. Start with Ag/AgCl electrode and its solder joint to a silver extension wire for C, and a silver wire on X. The tips of the stainless steel leads from C and X are out of the water, as is the transmitter body. We start recording M1542138183.ndf. We get this overview from 1000-1500 s. At time 1600 s we raise the solder joint in the C electrode above the water. We now have only a silver wire tip and an Ag/AgCl pellet with its attached silver wire within the saline. We get this from 1700-2200 s. From 2330-2445 s we are removing the Ag/AgCl pellet, scraping the silver wires, cutting off their tips, and replacing in saline, so we have two silver wires in water with no solder joints immersed. We get this from 3100-3600 s.

[15-NOV-18] Three charging A3028T-R drawing 15 μA today. But we note that the charging voltage is 4.1 V. We turn up to 4.2 V and see 45 μA. We check charge voltage with multimeter and get 4.21 V. Poaching transmitters C210.7, and E210.25, C206.157, 100% reception, response to 20-MΩ sweep correct.

[16-NOV-17] Three charging transmitter T19-21 consume 5 μA but we find that the charging voltage has dropped to 4.1 V. Increase to 4.2 V and see 35 μA. Remove from charger, turn on, place in beaker of water in faraday enclosure to discharge. Meanwhile, we have T209.19-22 encapsulated. Response to 20-MΩ sweep correct, noise ≤5 μV. We place on charger. Total input current 747 μA. Leave to charge for the weekend. Poaching transmitters C210.7, and E210.25, C206.157, 100% reception, battery voltages 2.70 V, 2.81 V, and 2.54 V respectively. We record from our A3028U 0-160 Hz transmitter with two silver wires in saline for 4500 s. We obtain this plot.

[27-NOV-18] Devices T19-21, A3028T-R, charging with 4.3 V, total current 170 μA. Poaching transmitters E210.25, C210.43, C210.53 ID, reception, VBAT, and rms noise uV: 25 99.85 2.77 4.6 43 100.00 2.70 11.3 56 97.46 2.68 10.2. We solder two teflon-insluted 125-μm diameter 316SS leads to U204.68 and two Ag/AgCl pellet electrodes to U204.69, both 512 SPS DC-160 Hz transitters. We fasten the transmitters outside a beaker of 1% saline, their leads passign over the rim of the beaker and down into the fluid. None of the leads are touching one another. Only the tips of the stainless steel leads are in the water. We place in our faraday enclosure and start continuous recording at 12 pm.

[28-NOV-18] Poaching transmitters E210.25, C210.43, C210.53 ID, reception 100%. Devices T19-21, A3028T-R, charging with 4.3 V, total current 60 μA. Remove from charger, each was taking 20 μA. The BAS116LPH4 drops 0.57 V at 20 μA, so batteries are getting 4.3−2×0.57 = 3.16 V through 1 kΩ. Remove U204.68 and 69 from faraday enclosure and turn off. Turn on T19-21 and place in faraday enclosure to monitor discharge. We analyze U204.68 and 69 twenty-two hour recording, extracting all events with power more than twice the average. We obtain thirteen events, all on channel 68. Nine are like the picture below.

Figure: Vibration Artifact of Steel Wire Tips in Saline.

Two are more vigorous oscillations that occur when we open the cage to remove the transmitters, see here. Two are glitches.

[13-DEC-18] Poaching transmitters T19, T20, T21, E210.25, C210.43, C210.53 response to 2-MΩ sweep correct. Note poor reception from T19-21 in 60°C water in faraday enclosure when first removed from oven. After ten minutes, water has cooled to 45°C, reception is 100% from all.